From Halopedia, the Halo wiki
Verivorr, also nicknamed Keelbugs, are a species of insectoid aliens created by the Forerunner rate of Lifeworkers to serve as living tools in the maintenance of their megastructures. Verivorr were adapted from a species found on a planet that was later infested by the Flood, and purified by the Halo Array. The verivorrserve their installations as biological maintenance technicians, and have their biology optimised for nutritional value and ensuring equilibrium in the ecosystems they are charged with maintaining. They do this by cleaning up corpses and other biological debris. They can also serve as guardians in a limited sense, and are known to be aggressive to external interlopers as part of an ecological first-line defence.
The keelbugs were originally designed during the production of Halo: Combat Evolved. They were first revealed in the behind-the-scenes documentaries on the Halo 2 Limited Collector's Edition disc, in which they were elaborated on as intended to be used for the purposes of saving on game memory by cutting up dead bodies and carrying them away.
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